The present invention relates to new and advantageous bonding compositions which are particularly useful for bonding wood and masonry. The invention also relates to the bonded articles thereby produced.
Phenol-aldehyde resins, particularly phenol-formaldehyde resins and many modifications of these have long been used as strong, water-resistant adhesives for making plywood and other bonded wood products. The curable intermediate stage resins useful in adhesive compositions of this class comprise two general types, those basically of novolac or bisphenol kind of structure but which have reactive alkylol groups on the aromatic rings, prepared by reacting phenol with an aldehyde in the presence of an acidic condensation catalyst, and resoles, particularly those having a preponderance of alkylol groups in ortho relationship to a phenolic hydroxyl, which are made by reacting phenol with aldehyde in the presence of a neutral or basic catalyst. Both types are curable to insoluble, infusible resins, usually by application of heat and, particularly in the case of those of alkylolated novolac structure, by reaction with additional aldehyde or other reactive cross-linking agent depending upon the structure of the resin. Acidic substances usually enhance the rate of cure.
Hydraulic cements such as portland cement have been combined with such curable resins, usually in either a very large or a very small proportion to obtain respectively a modified cement or a modified resin depending upon the proportion used. For example, Lefebure, British Pat. No. 231,242, Mar. 10, 1925, describes the addition of very small amounts of curable phenol-formaldehyde resin of the order of 0.5-10 percent to portland cement, along with water to set the cement, and heating the mixture to obtain a hard solid capable of being polished to a smooth surface. An example of the other kind of mixture known to the art in this area is disclosed by Thompson, U.S. Pat. No. 3,502,610. This patent describes the addition of 2-6 percent by weight of portland cement to resorcinol-formaldehyde resins to improve their molding properties and their resistance to water. Larger quantities of cement are said to produce mixtures which cure too fast and have poor physical properties.
Murata et al. in U.S. Pat. No. 3,666,703 describe a foundry core sand binder composition comprising a strongly alkaline aqueous phenol-formaldehyde resin, a relatively large proportion of a cement, and a substantial quantity of an alkaline accelerator. The particular type of intermediate resin shown is defined as unique for the purpose and other, more conventional types of phenol-formaldehyde intermediate resin are described as unsuitable for this use.